Bismuth method of abandoning a well

ABSTRACT

A well abandonment tool for deployment in a well tubing, comprising an upper section, including a connector to allow the tool to be deployed on slickline or wireline a housing including a chamber containing bismuth a receiver and processor, capable of receiving a signal from the surface to actuate a permanent sealing process a lower section, including a release means capable of releasing the upper section of the tool from a lower section of the tool a tubing cup seal capable to making a seal against the inside of the well tubing to contain moltenbismuth until it solidifies a tubing bridge plug or anchor capable of securing the tool inside the well tubing the tool also including a heat source capable of melting the bismuth to a flowable state, actuated by the receiver and processor such that when the tool has been secured in the well tubing, the bismuth melting process can be initiated, and the upper housing released from the lower housing to recover the upper housing, and bismuth being melted by the heating means and caused to flow into the well tubing above the tubing cup seal to form a plug.

Over the past 20 years or so a large number of offshore structures havebeen constructed which are now or will soon be exhausted and will needto be abandoned. These offshore structures may comprise productionplatforms which are either steel or concrete structures resting on thesea bed or floating platforms. Numerous conduits are connected to theseoffshore structures to carry the various fluids being gas, oil or wateretc., which are necessary for the production of oil and/or gas from thewell.

In abandoning a well, consideration has to be given to the potentialenvironmental threat from the abandoned well for many years in thefuture.

In the case of offshore structure there is usually no rig derrick inplace which can be used to perform the required well abandonmentprocedure. Therefore it is typically necessary to install a new derrickor alternatively a mobile derrick can be positioned above the well. Thisrequirement adds considerable expense to the task of abandoning theoffshore well, compared to a land based well.

A typical production well will comprise a number of tubular conduitsarranged concentrically with respect to each. The method of abandoningthe well which is presently known in the art involves the separatesealing of each of the concentric conduits which requires a large numberof sequential steps.

In the abandonment method known in the art the first step is to seal thefirst central conduit usually by means of cement or other suitablesealant. The first annular channel between the first and second conduitsis then sealed and the first central conduit is then cut above the sealand the cut section is removed from the well.

The second annular channel between the second and third conduits is thensealed and the second conduit cut above the seal and the cut section isremoved from the well.

This process is repeated until all the conduits are removed. The numberof separate steps required is typically very large indeed and the numberof separate operations is five times the number of conduits to beremoved. This adds considerably to the cost of the well abandonment dueto the time taken and the resources required at the well head.

It is the purpose of the present invention to provide a method ofabandoning a well which avoids the disadvantageous and numerousoperations which are required by the existing known methods. This willgreatly reduce the costs of safely abandoning a well. It is a furtherobjective of the invention to provide a method of abandoning a wellwithout the requirement of a rig which involves significant expenseparticularly in subsea based wells.

It is a further advantage of the invention to form a metal seal insidethe tubing inside the well.

According to the present invention there is provided a method ofabandoning a well, by using a tool loaded with thermite to provide aheat source and bismuth alloy fill the annular space around the thermiteheated tube.

According to another aspect of the present invention the ignitor iselectrically based and initiates a thermal ignitor when it receives acoded acoustic signal from a transmitting tool

According to another aspect of the present invention multiple bismuthmetal to metal seals can be placed on top of each other to make a metalto metal seal of unlimited length.

According to a further aspect of the invention the ignitor could includea secondary back up such as a timer in addition to the electrical wetconnector.

According to a further aspect of the invention the ignitor could includea secondary back up such as a hydrostatic pressure switch in addition tothe electrical wet connector.

According to a further aspect of the invention the ignitor could includea secondary low temperature alloy part which has to melt to operate aswitch in addition to the electrical wet connector.

According to a further aspect of the invention the bismuth meltingmethod could be an electric heating element

According to a further aspect of the invention, the bismuth in theretrievable running tool could provide the connecting means to thebridge plug, so when it melts the running tool is automatically releasedfrom the bridge plug.

According to a further aspect of the invention the bismuth forms a solidplug inside the tubing.

According to a further aspect of the invention multiple runs can beperformed to make the plug as long as required

According to the present invention there is provided a method of in asingle trip into the well, set a bridge plug, melt bismuth alloy,deposit the alloy on top of the bridge plug, release from the plug andreturn tool to surface.

According to a further aspect of the invention there the tool could beattached to the bridge plug by the low temperature alloy and when it isheated, the tool automatically releases itself from the bridge plug

According to a further aspect of the invention, there is provided aheating element to heat the convert the alloy from solid to liquid

According to a further aspect of the invention, a flux is releasedtogether with the molten bismuth to improve the bonding of the bismuthto the steel tubulars and the top of the bridge plug

According to a further aspect of the invention, bismuth beads aredeposited on the heat source

According to a further aspect of the invention, bismuth beads areconveyed in a container above the heat source

According to a further aspect of the invention, bismuth beads aredeposited from surface using gravity

According to a further aspect of the invention, bismuth is cast aroundthe heating element.

According to a further aspect of the invention the heat source could bethermite

Thus by means of the method according to the invention a very long metalto metal seal can be placed in the well tubing or well casing.

References to bismuth include alloys of bismuth capable of being melted,flowing to seal a region, and solidifying to provide a permanent seal.

The following is a more detailed description of an embodiment accordingto invention by reference to the following drawings in which:

FIG. 1 . is a section side view of a well showing the tubing inside thewell, a tool deployed on slickline or wireline, the tool consisting atubing anchor, a tubing cup seal, a thermite heat housing, a shearrelease, a bismuth store housing, an electronics circuit, a batterypack, an acoustic receiver and a connector to the wireline or slickline.

FIG. 2 is a view similar to FIG. 1 , with the anchor set, the thermiteheat tube activated, and the upper tool assembly sheared off and thebismuth falling by gravity into the annular space around the thermiteheat tube.

FIG. 3 is a view similar to FIG. 2 with a new thermite heat housing, ashear release, a bismuth store housing, a electronics circuit, a batterypack, an acoustic receiver and a connector to the wireline or slicklineto be latched onto the first thermite heat tube previously set in thewell with the bismuth seal between the thermite housing and the welltubing.

FIG. 4 is a similar view to FIG. 4 , with the second tool string latchedonto the first tool string.

FIG. 5 is a view similar to FIG. 4 , with the second thermite heat tubeactivated, and the second upper tool assembly sheared of and the bismuthfalling by gravity into the annular space around the second thermiteheat tube and on top of the first bismuth plug.

FIG. 6 is a section side view of a well with another embodiment of theinvention, in its position to be activated

FIG. 7 . is a similar view to FIG. 6 with the tool having a completesection side view of its internal components.

FIG. 8 is a section side view of a well with the tool in a secondreleased position from the bridge plug.

FIG. 9 is a similar view to FIG. 8 with the tool having a completesection side view of its internal components.

FIG. 10 is a section side view of a well and tool assembly with a secondembodiment of the invention, in its position to be activated

FIG. 11 is a section side view of a detail highlighted in FIG. 10

FIG. 12 is a similar view to FIG. 10 with the upper half of the toolseparated from the lower half.

FIG. 13 is a similar view to FIG. 12 , with all the low temperaturealloy deposited on top of the bridge plug and the upper half of the toolreturning to surface.

Referring to FIGS. 1 to 5 , there is shown a well tubing 1. Inside thetubing is a tool assembly 2, consisting of a tubing anchor 3, a cup seal4, a tubular housing 5 containing thermite 6 and an ignitor 7, twoelectrical cables 8 and connectors 9, a shear pin 10, a second housing11 inside which is bismuth alloy pellets 12, two electrical cables 13linking the connectors 9 to a relay 13, the relay being part of anelectrical circuit 14 which consists of a pressure sensor which onlyallows the tool to operate below a pre-defined depth in the well, a setof lithium batteries 15 each 30 amps and 4.4 volts arranged in seriesand an acoustic transmitter/receiver, all attached to a slickline orwireline 16

In operation, the assembly would be lowered in the well, once at therequired setting depth, the tubing stop 3 would be set by rapidlystopping the downward movement of the wireline. This is awell-established practice and well understood by a well operativeskilled in deploying slickline tools. Once set the wireline would bepull tested to confirm that the anchor is set.

A signal would be transmitted down the wireline, or an acoustic signalwould be transmitted from surface if deployed on slickline, there arefour operating modes: standby, ready, arm, and fire.

The goal is for safety and security, the receiver must receive theproper commands in the proper sequence in order to initiate the burn.

Before it can do anything, the pressure switch safety interlock has tobe activate. Once that happens, it goes to ready mode, it will receiveanything it hears, but it is looking for specific commands and apreamble and post amble (framing bytes). Unless all these conditions aremet, the processor of the electrical circuit causes the tool to ignorethe transmission.

So first the Ready command is sent, then “arm”, then “fire”. On Fire,the relay 13 latches on, and applies power which comes from 3×4.4 volt30 amp batteries 15 in series to the initiator 7 and the retardedthermite does a slow burn.

The entire housing 5 heats up to 600-1000C. A temperature sensor 17,sends a signal back to the circuit 18 and this transmits thisinformation back to surface.

Tension would be applied to the wireline to shear the shear pin 10, orwireline jar (not shown) would apply the shock load to shear the shearpin. The tool housing 11 would come free 20, and the bismuth insidewould fall out of the inside of the housing due to gravity and fall intothe annular space 21 and form a solid metal to metal seal from the cupseal 4 to just below the top 22 of the tool remaining in the well, thedisconnected upper half of the tool 23 can be recovered to surface.

Additional bismuth beads could be supplied from surface by feeding thebeads 40 into tubing and letting them fall under gravity to land on topthe thermite heater 6, if the housing 11 cannot transport sufficientbeads to fully cover the thermite heater. Alternatively, all the bismuthto be used in the process could be supplied from the surface to fallonto the heating element of the deployed tool.

A second tool assembly 24 can be deployed to increase the length of themetal to metal seal. This tool assembly consists of a collet 30, atubular housing 5 containing thermite 6 and an ignitor 7, two electricalcables 8 and connectors 9, a shear pin 10, a second housing 11 insidewhich is bismuth alloy pellets 12, two electrical cables 13 linking theconnectors 9 to a relay 13, the relay being part of an electricalcircuit 14 which consists of a pressure sensor which only allows thetool to operate below a pre-defined depth in the well, a set of lithiumbatteries 15 each 30 amps and 4.4 volts arranged in series and anacoustic transmitter/receiver, all attached to a slickline or wireline16

The collet 30 latches onto the profile 31, and then the sequence ofigniting the thermite and releasing the bismuth into the annular spaceis repeated, the new melted bismuth falls on top of the previous, nowsolidified bismuth 32 from the first run, now the bismuth seal is twicethe original length 33. This could be repeated again to further increasethe metal to metal seal to be as long as required.

Referring to FIGS. 6 to 9 there is shown a section side of an oil or gaswell with internal surface of the production tubing 101 shown as asingle line (for clarity).

The tool is conveyed on electric wireline 102, and consists of aconventional connector 103 incorporating a standard release joint.Inside the tool is a telemetry package 104 which also includestemperature sensors and casing collar locator for depth control. Theupper housing 105 of the tool contains a heating element 106 and thevoid space around it inside the housing is filled with low temperaturealloy 107

When the tool is at the required setting depth, it is rapidly stopped,this deceleration causes a weighted rod 108 to shear a pin and unlockthe slips 109, which are spring loaded 110, resulting in the slipslocking the bridge plug to the tubing ID. A cup seal 111 provides apressure seal, and more importantly a place for the molten bismuth torest.

After the bridge plug is set, the tool is jarred up to release if from aS type release tool 113. The heating element 6 is then turned on andmolten bismuth flows out of ports 112 and comes to rest on top of theseal 111and around the lower half 114 of the S type release tool

Once all the bismuth has been discharged the upper half of the toolassembly is returned to surface.

Referring to FIGS. 10 to 13 , there is shown another embodiment of theinvention, in this version, there is no release tool, low temperaturealloy 120 is used to lock the lower assembly 121 to the upper assembly122. It is cast into a recess 123 on the lower assembly and 124 on theupper assembly. When the heating element 125 is turned on, it melts thelow temperature alloy which results in the two halves of the tool121,122 separating, the molten bismuth is immediately above the cup seal126. As the heating element goes to the very bottom of the assembly 122there is no risk of the assembly 122 getting stuck by solidified lowtemperature alloy. Once all the low temperature alloy is deposited 127on top of the bridge plug 128, the upper tool assembly 122 is returnedto surface.

1. A well abandonment tool for deployment in a well tubing, comprising:an upper section, including, and a connector to allow the tool to bedeployed on slickline or wireline, a housing including a chambercontaining bismuth, and a receiver and processor, capable of receiving asignal from the surface to actuate a permanent sealing process; and alower section, including: a release means capable of releasing the uppersection of the tool from a lower section of the tool, a tubing cup sealcapable to making a seal against the inside of the well tubing tocontain molten bismuth until it solidifies, and a tubing bridge plug oranchor capable of securing the tool inside the well tubing; the toolalso including a heat source capable of melting the bismuth to aflowable state, actuated by the receiver and processor; such that whenthe tool has been secured in the well tubing, the bismuth meltingprocess can be initiated, and the upper housing released from the lowerhousing to recover the upper housing, and bismuth being melted by theheating means and caused to flow into the well tubing above the tubingcup seal to form a plug.
 2. A tool according to claim 1, wherein thereceiver is an acoustic receiver capable of receiving a coded acousticsignal from a transmitting tool.
 3. A tool according to claim 1, whereinthe receiver receives electrical signals conducted by a wire connectionfrom the surface.
 4. A tool according to claim 1, wherein the heatsource is a housing containing thermite, provided with a ignitor and abattery pack to initiate a thermite reaction.
 5. A tool according toclaim 1, wherein the heat source is an electric element.
 6. A toolaccording to claim 1, wherein the ignitor includes a secondary back upsuch as a timer in addition to the electrical wet connector.
 7. A toolaccording to claim 1, wherein the ignitor includes a secondary back upsuch as a hydrostatic pressure switch in addition to the electrical wetconnector.
 8. A tool according to claim 1, wherein the ignitor includesa secondary low temperature alloy part which has to melt to operate aswitch in addition to the electrical wet connector.
 9. A tool accordingto claim 1, wherein the bismuth in the retrievable running tool couldprovide the connecting means to the lower section, so when it melts therunning tool is automatically released from the lower section.
 10. Atool according to claim 1, wherein a flux is provided, releasabletogether with the molten bismuth to improve the bonding of the bismuthto the steel tubulars and the top of the lower section.
 11. A toolaccording to claim 1, wherein bismuth beads are conveyed in a containerabove the heat source.
 12. A tool according to claim 1, wherein bismuthis cast around the heat source for deployment.
 13. A method of using atool according to claim 1, including depositing bismuth beads on theheat source.
 14. A method of using a tool according to claim 13, whereinbismuth beads are deposited from surface using gravity.
 15. A method ofoperating in a well using a tool according to claim 1, includingdeploying multiple tools to produce multiple bismuth metal to metalseals placed on top of each other to make a metal to metal seal ofunlimited length.